ET 12-0023, 10 CFR 50.46 Thirty Day Report of ECCS Model Changes

10 CFR 50.46 Thirty Day Report of ECCS Model Changes

ML12298A504
Person / Time
Site:	Wolf Creek
Issue date:	10/15/2012
From:	Broschak J Wolf Creek
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
ET 12-0023
Download: ML12298A504 (8)

Text

W> LF CREEK ' NUCLEAR OPERATING CORPORATION October 15, 2012 John P. Broschak Vice President Engineering ET 12-0023 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555

Reference:

Westinghouse Letter LTR-LIS-12-515, dated September 20, 2012, 10 CFR 50.46 Notification and Reporting for Fuel Pellet Thermal Conductivity Degradation and Peaking Factor Burndown

Subject:

Docket No. 50-482: 10 CFR 50.46 Thirty Day Report of ECCS Model Changes Gentlemen:

In the above reference, Westinghouse Electric Company submitted to Wolf Creek Nuclear Operating Corporation (WCNOC) a mid-year notification of 10 CFR 50.46 reporting information pertaining to the evaluation to estimate the effect of fuel pellet thermal conductivity degradation (TCD) and assembly power/peaking factor burndown in the Wolf Creek Generating Station (WCGS) Appendix K Large-Break Loss-of-Coolant Accident (LOCA) analysis. The estimated effects for WCGS were determined based on the bounding results from available sensitivity calculations for other plants. WCNOC has reviewed the reference, and has concluded that the cumulative effect of changes to, or errors in, the evaluation model on the limiting Large Break LOCA Peak Cladding Temperature (PCT) is significant, as defined in 10 CFR 50.46.

Therefore, this report of the Emergency Core Cooling System (ECCS) Evaluation Model changes is being submitted within 30 days according to the reporting requirements set forth in 10 CFR 50.46(a)(3)(ii), as clarified in Section 5.1 of WCAP-13451, "Westinghouse Methodology for Implementation of 10 CFR 50.46 Reporting."

Attachment I provides an assessment of the specific changes to the Westinghouse ECCS Evaluation Model for Large Break LOCAs identified by Westinghouse in the reference.

Attachment II provides an update of the WCGS PCT margin utilization for the Large Break LOCA evaluation model. The PCT value determined in the Large Break LOCA analysis of record, combined with all of the PCT allocations, remains below the 10 CFR 50.46 regulatory limit of 2200 degrees Fahrenheit. Therefore, WCGS is in compliance with 10 CFR 50.46 requirements. However, due to the age (1992) of the Large Break LOCA analysis of P.O. Box 411 / Burlington, KS 66839 / Phone: (620) 364-8831 An Equal Opportunity Employer M/F/HCNET

ET 12-0023 Page 2 of 2 record and the number of PCT assessments currently tracked on the Large Break LOCA PCT summary sheet, WCNOC is exploring options to perform a reanalysis, based on the approved Automated Statistical Treatment of Uncertainty Method (ASTRUM), with incorporation of the effect of the fuel pellet thermal conductivity degradation. Depending on the option selected, a more definitive reanalysis schedule will be available in the first quarter of 2013.

This letter contains no commitments. If you have any questions concerning this matter, please contact me at (620) 364-4085, or Mr. Gautam Sen at (620) 364-4175.

Sincerely, John P. Broschak JPB/rlt Attachment I - Assessment of Changes to the Westinghouse Emergency Core Cooling System (ECCS) Evaluation Model for Large Break Loss of Coolant Accidents (LOCA)

Attachment II - Emergency Core Cooling System (ECCS) Evaluation Model Peak Cladding Temperature (PCT) Margin Utilization - Large Break LOCA cc: B. J. Benney (NRC), w/a E. E. Collins (NRC), w/a N. F. O'Keefe (NRC), w/a Senior Resident Inspector (NRC), w/a

Attachment I to ET 12-0023 Page 1 of 3 ASSESSMENT OF CHANGES TO THE WESTINGHOUSE EMERGENCY CORE COOLING SYSTEM (ECCS) EVALUATION MODELS FOR LARGE BREAK LOSS OF COOLANT ACCIDENTS (LOCA)

Non-Discretionary Chanaes With Peak Claddin_ Temperature (PCT) Impact "REBASELINE" OF THE ANALYSIS OF RECORD (AOR), WHICH REFLECTS THE EFFECTS OF UPDATES TO THE CODES AND METHODS BASH-EM EVALUATION OF FUEL PELLET THERMAL CONDUCTIVITY DEGRADATION Non-Discretionary Changes With No PCT Impact None EnhancementslForward-Fit Discretionary Chanqes None

Attachment I to ET 12-0023 Page 2 of 3 "REBASELINE" OF THE ANALYSIS OF RECORD (AOR), WHICH REFLECTS THE EFFECTS OF UPDATES TO THE CODES AND METHODS (Non-Discretionary Change with PCT Impact)

Background

A method has been developed to extend BASH Evaluation Model transients beyond the point at which downcomer boiling is predicted to occur in BASH by correlating the boiling induced reduction in downcomer driving head to a corresponding reduction in the core inlet flooding rate. This approach, which is referred to as the LOCBART transient extension method (TEM), is used to ensure adequate termination of the fuel rod cladding temperature and oxidation transients predicted by LOCBART as required to demonstrate compliance with the pertinent acceptance criteria of 10 CFR 50.46. The LOCBART TEM has been reviewed and approved by the NRC, in accordance with Reference 1.

The rebaseline penalty is a combination of the new code versions, changes in the resulting core inlet flooding rate, and implementation of the LOCBART TEM. This represents a non-Discretionary Change in accordance with Section 4.1.2 of WCAP-13451.

Affected Evaluation Model(s) 1981 Westinghouse Large-Break LOCA Evaluation Model with BASH Estimated Effect The estimated effects for Wolf Creek were determined to be 87 0 F, based on the bounding results from available sensitivity calculations for other plants. These calculations incorporated the approved LOCBART TEM and met the Limitations and Conditions in Reference 1.

References

1. WCAP-10266-P-A, Revision 2, Addendum 3-A, Revision 1, "Incorporation of the LOCBART Transient Extension Method into the 1981 Westinghouse Large Break LOCA Evaluation Model with BASH (BASH-EM)," October 2007.

BASH-EM EVALUATION OF FUEL PELLET THERMAL CONDUCTIVITY DEGRADATION (Non-Discretionary Change with PCT Impact)

Background

Evaluations have been completed to estimate the effect of fuel pellet thermal conductivity degradation (TCD) on peak cladding temperature (PCT) for analyses using the 1981 Westinghouse Large-Break Loss-of-Coolant Accident Evaluation Model with BASH (BASH-EM) with the LOCBART Transient Extension Method. These evaluations

Attachment I to ET 12-0023 Page 3 of 3 utilized fuel rod performance input from a version of the PAD code that accounts for pellet TCD and considered the beneficial effects of assembly power and peaking factor burndown resulting from the depletion of fissionable isotopes. This change represents a Non-Discretionary Change in accordance with Section 4.1.2 of WCAP-1 3451.

Affected Evaluation Model(s) 1981 Westinghouse Large-Break LOCA Evaluation Model with BASH Estimated Effect The estimated effect was determined on a plant-specific basis. The peaking factor burndown used in the evaluation is provided in Table 1; it is conservative for the current cycle and will be validated as part of the reload design process. Wolf Creek Nuclear Operating Company and its vendor, Westinghouse Electric Company, LLC, utilize processes which ensure that the corresponding LOCA analysis input parameters conservatively bound the as-operated plant values.

Table 1: Peaking Factors Assumed in the Evaluation of TCD Rod Burnup 12 FAH( ' ) FQ(1)

(GWD/MTU) 0 1.65 2.50 30 1.65 2.50 60 1.40 2.00 62 1.40 2.00

1. Includes uncertainties.

Hot assembly average power (PHA) follows the same burndown since it is a function of FAH.

Attachment II to ET 12-0023 Page 1 of 3 EMERGENCY CORE COOLING SYSTEM (ECCS) EVALUATION MODEL PEAK CLADDING TEMPERATURE (PCT) MARGIN UTILIZATION LARGE BREAK LOCA PCT MARGIN UTILIZATION Evaluation Model: 1981 EM with BASH Fuel: 17x17 V5H w/IFM, non-IFBA, 275 psig Peaking Factor: FQ=2.50, FdH=1.65 SG Tube Plugging: 10%

Power Level: 3565 MWth Limiting transient: Cd=0.4, Min. SI, Reduced Tavg LICENSING BASIS Clad Temp (*F) Ref. Notes Analysis of Record PCT 1916 0 F 1 (a)

MARGIN ALLOCATIONS (APCT)

A. PRIOR PERMANENT ECCS MODEL ASSESSMENTS

1. Structural Metal Heat Modeling -25 8

2. LUCIFER Error Corrections -6 10

3. Skewed Power Shape Penalty 152 11

4. Hot Leg Nozzle Gap Benefit -136 11

5. SATAN-LOCTA Fluid Error 15 2

6. LOCBART Spacer Grid Single-Phase Heat Transfer Error 15 9

7. LOCBART Vapor Film Flow Regime Heat Transfer Error 9 12

8. LOCBART Cladding Emissivity Errors 6 13

9. LOCBART Radiation to Liquid Logic Error Correction 17 14

10. LOCBART Pellet Volumetric Heat Generation Rate 45 15 B. PLANNED PLANT CHANGE EVALUATIONS

1. Loose Parts Evaluation 20 3

2. Effects of Containment Purging 0 4

3. Cycle 10 Fuel Assembly Design Changes 95 5

4. Fuel Rod Crud 0 6 C. 2012 PERMANENT ECCS MODEL ASSESSMENTS

1. PWROG TCD EVALUATION - Rebaseline of AOR 87 16 (e)

2. PWROG TCD Evaluation - Effect of TCD and Assembly 0 16 (e)

Power/Peaking D. TEMPORARY ECCS MODEL ISSUES 0 E. OTHER

1. Cold Leg Streaming Temperature Gradient 0 8 (b)

2. Rebaseline of AOR (12/96) -63 9 (c)

3. LOCBART Zirc-Water Oxidation Error 28 7 (d)

LICENSING BASIS PCT + MARGIN ALLOCATIONS PCT = 2175°F

Attachment II to ET 12-0023 Page 2 of 3 CUMULATIVE ABSOLUTE MAGNITUDE OF PCT CHANGES E'I APCT = 87°F SINCE LAST 30-DAY REPORT (LETTER ET 07-0021)

References:

1. Westinghouse Topical Report WCAP-13456, "Wolf Creek Generating Station NSSS Rerating Licensing Report," October 1992.

2. Westinghouse to WCNOC letter SAP-97-102, "Wolf Creek Nuclear Operating Corporation, Wolf Creek Generating Station, 10 CFR 50.46 Annual Notification and Reporting," February 17, 1997.

3. Westinghouse to WCNOC letter SAP-90-148, "Wolf Creek Nuclear Operating Corporation, RCS Loose Parts Evaluation," April 18, 1998.

4. Westinghouse to WCNOC letter SAP-94-102, "Containment Mini purge Isolation Valve Stroke Time Increase," January 12, 1994.

5. Westinghouse to WCNOC letter 97SAP-G-0009, "Wolf Creek Nuclear Operating Corporation, Wolf Creek Generating Station, Safety Assessment for the Wolf Creek Generating Station with ZIRLO TM Fuel Assemblies," February 7, 1997.

6. Westinghouse to WCNOC letter 97SAP-G-0075, "Wolf Creek Nuclear Operating Corporation, Wolf Creek Generating Station, Wolf Creek Crud Deposition/Axial Offset Anomaly Safety Evaluation," September 29, 1997.

7. Westinghouse to WCNOC letter OOSAP-G-0006, "Wolf Creek Nuclear Operating Corporation, Wolf Creek Generating Station, Wolf Creek Cycle 12 LOCA Current Limits," February 10, 2000.

8. Westinghouse to WCNOC letter SAP-93-701, "Wolf Creek Nuclear Operating Corporation, Wolf Creek Generating Station, 10 CFR 50.46 Notification and Reporting Information," January 25, 1993.

9. Westinghouse to WCNOC letter SAP-99-148, "Wolf Creek Nuclear Operating Corporation, Wolf Creek Generating Station, 10 CFR 50.46 BART/BASH Evaluation Model Mid-Year Notification and Reporting for 1999," September 22, 1999.

10. Westinghouse to WCNOC letter SAP-94-703, "Wolf Creek Nuclear Operating Corporation, Wolf Creek Generating Station, 10 CFR 50.46 Notification and Reporting," February 8, 1994.

11. Westinghouse to WCNOC letter SAP-95-716, "Wolf Creek Nuclear Operating Corporation, Wolf Creek Generating Station, LOCA Axial Power Shape Sensitivity Model," August 14, 1995.

12. Westinghouse to WCNOC letter SAP-00-1 18, "Wolf Creek Nuclear Operating Corporation, Wolf Creek Generating Station, 10 CFR 50.46 Appendix K (BART/BASH/NOTRUMP) Evaluation Model, Mid-Year Notification and Reporting for 2000," June 30, 2000.

13. Westinghouse to WCNOC letter SAP-00-1 50, "Wolf Creek Nuclear Operating Corporation, Wolf Creek Generating Station, 10 CFR 50.46 BART/BASH Evaluation Model Mid-Year Notification and Reporting for 2000," December 2000.

14. Westinghouse to WCNOC letter SAP-02-32, "10 CFR 50.46 BART/BASH Evaluation Model Mid-Year Notification and Reporting for 2002," June 2002.

15. Westinghouse to WCNOC letter LTR-LIS-07-312, "10 CFR 50.46 Reporting Text for LOCBART Version 37.0 Issues and Revised PCT Rackup sheets for Wolf Creek," May 14, 2007

16. Westinghouse to WCNOC letter LTR LIS-12-515, "Wolf Creek, 10 CFR 50.46 Notification and Reporting for Fuel Pellet Thermal Conductivity Degradation and Peaking Factor Burndown,"

September 20, 2012.

Notes:

(a) An evaluation was performed to support removal of the transition core penalty for Cycle 12 (Ref. 7).

Attachment II to ET 12-0023 Page 3 of 3 (b) A PCT benefit of < 2.5 0 F was assessed, however, a benefit of 0°F will be tracked for reporting purposes.

(c) This previously unclaimed benefit was realized through prior rebaseline of the limiting case.

(d) This assessment is a function of analysis PCT plus certain margin allocations and as such may increase/decrease with margin allocation changes.

(e) This effect was estimated based on the bounding value from the available plant-specific calculations.